Method of stripping rhodium plating



I Patented Oct; 13, 1936 I UNITED STATES NIETHOD OF STRIPPING RHODIUM PLATING Karl- Schumpelt, Union, N. J., asslgnor to Baker & Company, Inc., a corporation of New Jersey No Drawing. Original application April 20, 1935, Serial No. 17,390. Divided and this applicatio May 12, 1936, Serial No. 79,270

13 Claims. (01. 75-101) This application is a division of my copendin application Serial No. 17,390, filed April 20, 1935.

The use of electrodeposited rhodium for protecting silverware, jewelry or silver plated arholes against tarnishing and scratching-or for producing a pleasing white and lustrous finish on certain metals suchas stainless steel, has become popular and extensive. However, it is desirable in some. cases to remove the rhodium platl0 ing, especially from silverware and other articles formed of or plated with silver, for various reasons.

Variousattempts have been made to remove the rhodium plating, forexample, electrolytically by 15 placing the article as the anode in acid solution. but the rhodium is so resistant to the action of acids that the silver or other metal of which the article is formed is injured or destroyed by the chemicals that have been used, so that such methods are impracticable. Therefore, it has been the general practice to remove the rhodium by grinding the rhodium plating from the article. This is a slow, laborious and expensive process, and great care and skill are necessary to prevent damage to the. article. Therefore a prime object of my invention is to provide a novel and improved practical, easy and inexpensive method of removing the rhodium plating without injuring the article.

30 Generally, in electrodepositing rhodium for the purpose above-mentioned, it has been found desirable to electrodeposit a layer of nickel on the article preliminary to applying the finish layer of rhodium so that the rhodium is deposited on 35 the nickel and a composite coating of nickel and rhodium results, and I contemplate the removing of rhodium plating by simply immersing the ar ticle in a solution containing an acid which will dissolve the nickel but which will not materially 40 attack the metal of which the article is formed,

for example silver. Also I contemplate forming on the surface or the article during the treatment thereof in the acid, a coating that will protect the metal of the article from attack by the acid 45 regardless of thelength of time that the article may remain in the acid. My method obviates the use of electric current and is inexpensive and safe in operation. 0 According to the present invention the meth 0d of stripping a composite coating ijormed ofa ,5 ing is formed of base metal. ischaracterized by treating said coated article with a solvent that will dissolve the base metal but will not attack the metal of the article or the outer coating of the layer, particularly a bath including hydrochloric acid and water wherein the acid predomi- 5 nates. Thus, in accordance with the invention the method of stripping a composite coating of a plurality of layers of nickel or rhodium from silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhol0.

dium, comprises the immersion of the coated article'in an acid bath comprising hydrochloric acid or acetic acid or both, and water, which bath will dissolve the nickel but will not attack the silver.

' mula in detail is o Hydrochloric acid 600cc.

Water a 400 cc.

Aluminum sulphate, about grams Sodium chloride, about 30 grams So far only inorganic acids which do not seriously attack silver have been specifically mentioned, although some organic acids which do not attack silver, such as acetic acid, may be used. Also acetic acid may be combined with hydrochloric acidas follows: e.

Hydrochloric acid 500 cc. Acetic acid; -l 200 cc.

Water a Y 300 cc. 40 Sodium chloride 30 grams In all of the formulae, the proportions of the components are not critical and may be widely varied.

The method is carried out at a temperature preferably ranging from 30 degrees C. to 70 degrees C;, and the time required for completion of the method depends upon the amount of the electrodeposited metal. The article being treated is permitted to remain in the solution until the nickel has'been dissolved and the rhodium flakes" off. The silver in the article is not damaged even where the article has engine turned surfaces, and in fact the silver is protected against iniury by a coating for example of silver chloride the solution.

The sodium chloride may bromitted where hydrochloric acid is present; and aluminum sulphate may be omitted although its presence is -desirable. Furthermore, other metal sulphates such as ferric sulphate may be substituted for the aluminum sulphate.

In all cases the acid does not attack or afl'ect the rhodium, but I have found that the acid solution permeates the rhodium coating which is usually extremely thin and then dissolves the layer of nickel beneath the rhodium. The removal oi. the nickel of course frees the rhodium from both the article and the nickel whereby the rhodium can be easily recovered.

After the nickel and rhodium have been removed irom the article, the surfaces of the article can be easily-polished.

Having thus described my invention, claim is:

1. The method of stripping a composite coating'of a plurality oi layers-o1 nickel and rhodium from a silver or silver' plated article wherein the nickel layer or layers constitute underplating for the rhodium, said method consisting in immersing the coated article in a bath comprising hydrochloric acid, water and small quantities of a metal sulphate and sodium chloride.

2. The method of stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhodium, said method consisting in immersing the coated article in a bath comprising hydrochloric acid, acetic acid, water, and a small quantity oi sodium chloride.

3. The method of stripping a composite coating of a plurality of layers of diilerent metals from a silver or silver plated article wherein the outer layer comprises one or more metals of the platinum group and the inner layer or layers is formed or base metal, consisting in immersing the article with the coating in hydrochloric acid, water and small quantities oi'a metal sulphate.

4. The method of stripping a composite coating of a plurality of layers of difierent metals from,

a silver or silver plated article wherein the outer layer comprises one or more metals of the platinum group and the inner layer or layers is formed of base metal, consisting in immersing the article with the coating in a bath comprising hydrochloric acid, acetic acid, water, and a small quantity or sodium chloride.

5. The method of stripping a composite coating of a'plurality of layers 'of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhodium, said method consisting in immersing the coated article in a bath comprising a mixture of hydrochloric acid and water wherein hydrochloric acid is the major portion.

6. The method or stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating. for the rhodium, said method consisting in immersing the coated article in a bath comprising a mixwhat 1' ture of hydrochloric acid and water wherein hydrochloric acid is the major portion and a small quantity or a metal sulphate.

7. The method of stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhodium, said method consisting in immersing the coated article in a bath comprising a mixture of hydrochloric acid and water wherein hydrochloric acid is the major portion and a small quantity of aluminum sulphate.

8. The method of stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhodium and said method consisting in immersing the coated article in a bath comprising a mixture of hydrochloric acid and water in the proportions of three-fifths of a liter of hydrochloric acid and two-fifths of a liter of water.

9. The method of stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhodium and said method consisting in immersing the coated article in a bath comprising a mixture of hydrochloric acid and water in the proportions of three-fifths of a liter of hydrochloric acid and two-fifths of a liter of water and about grams of aluminum sulphate.

1 10. The method of stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhodium, said method consisting in immersing the coated article in a bath comprising a mixture of hydrochloric acid and water wheren hydrochloric acid is the major portion, and acetic acid.

11. The method or stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhodium, said method consisting in immersing the coated article in a bath comprising a mixture of hydrochloric acid and water wherein hydrochloric acid is the major portion, and an organic acid that will not attack silver.

12. The method of stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver plated article wherein the nickel layer or layers constitute underplating for the rhodium and said method consisting in im mersing the coated article in a bath comprising a mixture of hydrochloric acid and water in the proportions of about one-half liter of hydrochloric acid, about one-third liter of water, and about one-fifth liter of acetic acid.

13. The method of stripping a composite coat-- ing of a plurality of layers of different metals from a silver or silver plated article wherein the outer layer comprises one or more metals of the platinum group and the inner layer or layers is formed of base metal, said method consisting in immersing the coated article in a bath comprising a mixture of hydrochloric acid and water wherein hydrochloric acid is the major portion.

KARL SCHUMPELT. 

